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Abstract
The ventral surfaces of translucent rocks from hot desert pavements often harbor hypolithic microbial communities, which are mostly dominated by cyanobacteria. The Namib Desert fog belt supports extensive hypolithic colonization of quartz rocks, which are also colonized by lichens on their dorsal surfaces. Here, we aim to evaluate whether lichens colonize the ventral surface of the rocks (i.e., show hypolithic lifestyle) and compare the bacterial composition of these coastal hypolithic communities with those found inland. Fungal DNA barcoding and fungal and bacterial Illumina metabarcoding were combined with electron microscopy to characterize the composition and spatial structure of hypolithic communities from two (coastal and inland) areas in the Namib Desert. We report, for the first time, the structure and composition of lichen-dominated hypolithic communities found in the coastal zone of the Namib Desert with extensive epilithic lichen cover. Lichen modified areoles with inverted morphology of the genus Stellarangia (three lineages) and Buellia (two lineages) were the main components of these hypolithic communities. Some of these lineages were also found in epilithic habitats. These lichen-dominated hypolithic communities differed in structural organization and bacterial community composition from those found in inland areas. The hypolithic lichen colonization characterized here seems not to be an extension of epilithic or biological soil crust lichen growths but the result of specific sublithic microenvironmental conditions. Moisture derived from fog and dew could be the main driver of this unique colonization.
Highlights
Life in desert soil is principally constrained by water availability
Stellarangia spp. (Fig. 1B-D) were the lichenized fungi more commonly found at epilithic locations, but species in Xanthoparmelia (Fig. 1E) and Buellia (Fig. 1F) were observed
Previous research has reported that the distribution of terricolous lichens in the Namib Desert depends on factors such as distance to the coast, elevation, climatic gradients, wind and sand force, substrate, and physiological adaptations [25, 47]
Summary
Open desert soils are relatively depauperate habitats that support low-biomass microbial communities [1]. The ventral surfaces of translucent rocks (mainly quartz or marble) often harbor hypolithic communities that constitute substantial standing biomass [2,3,4]. Hypolithic microbial communities are considered hotspots of primary productivity and organic matter accumulation in hyperarid deserts [5]. Under these translucent rocks, microbial communities exist in microrefugia with less stringent environmental conditions than open soils, where the overlying lithic substrate provides protection against high incident UV fluxes, generates thermal buffering, and enhances moisture availability [6]. Mossdominated hypolithic communities have been reported in the Mojave Desert [8] and in the cold Antarctic Dry
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